Schokolade
chocolate
Used as an indeclinable adjective to describe the flavor of chocolate. Often used when naming varieties or flavors.
Ich hätte gern ein Eis, die Sorte Schokolade bitte.
I'd like an ice cream, chocolate flavor please.

chocolate
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chocolate
Used as an indeclinable adjective to describe the flavor of chocolate. Often used when naming varieties or flavors.
Ich hätte gern ein Eis, die Sorte Schokolade bitte.
I'd like an ice cream, chocolate flavor please.

In this use, the noun 'die Schokolade' (chocolate) is placed like an adjective before another noun to specify its flavor or color. The word 'Schokolade' always remains unchanged and is not declined.
Ich esse am liebsten den Kuchen mit Schokolade-Glasur.
I like cake with chocolate glaze best.
This pattern—using a noun as an invariable adjective for flavor or color—is very common in German. It also works with other words such as 'Vanille' (vanilla), 'Zitrone' (lemon), or 'Orange' (orange).
Im Sommer trinke ich gern Wasser mit Zitrone-Geschmack.
In summer, I like drinking water with lemon flavor.
Whether flavor or color is meant is revealed by the noun that follows. If 'Schokolade' (chocolate) comes before foods like 'Eis' (ice cream), 'Pudding' (pudding), or 'Kuchen' (cake), it is about flavor. If it comes before things like 'Farbe' (color/paint), 'Stoff' (fabric), or 'Auto' (car), the color is meant.
Dieser Schokolade-Pudding schmeckt himmlisch.
This chocolate pudding tastes heavenly.
dark brown
'Schokolade' and 'dunkelbraun' can both describe a brown, dark color. 'dunkelbraun' is the normal and precise color term. 'Schokolade' as an indeclinable adjective compares the color to chocolate and sounds more like a variety or style label. It can also mean the flavor, so the context has to be clear. If you are only talking about the color, 'dunkelbraun' is usually more unambiguous.

Sie wählt für das Sofa die Farbe Schokolade.
She chooses the color chocolate for the sofa.
Meine Freundin hat im Urlaub einen dunkelbraunen Ledergürtel gekauft.
My friend bought a dark brown leather belt while on vacation.